1. Field of the Invention
The present invention relates to a method of designing a communications network comprising a physical network and a logical network, and to a method of managing the designed communications network. The designing method aims to have a system quickly and flexibly respond to, for example, the fluctuation of traffic using simple designing procedures by individually designing the topology and the capacity of the communications network. The managing method aims to shorten the time taken for selection of an applicable communications path in response to a request to connect a virtual path, and to enable the capacity to be altered, in response to a request to alter the capacity of a communications path, by quickly selecting one of a plurality of virtual paths defined between two nodes in the communications path.
2. Description of the Related Art
The present invention has been developed based on the following background. First, the concept of a logical network has been introduced into the concept of an ATM network, that is, forming a communication network of a new generation. Second, the topology and the capacity of the logical network can be flexibly set and independently controlled. Third, as communications networks grow in scale and communications services are vigorously diversified, it has become very hard to precisely estimate the traffic demand and characteristics accommodated in a communications network, and their values are subject to constant changes.
Thus, a conventional complicated optimization design method using a specific traffic pattern does not work effectively, and such a simple and flexible method of designing a communications network is needed which flexibly handles various traffic conditions. Since both a physical network and a logical network are required in designing a communications network, respective shares of both networks should be carefully considered to design the simplest possible network.
According to the conventional technology of designing a communications network comprising a physical network and a logical network, the logical network is optimally designed, first based on a specific traffic condition and request quality, and then in accordance with the result the physical network is designed for optimal accommodation. Accordingly, if a traffic condition or a request quality of a service is changed, then the above described design cycle must be reconsidered from the very beginning, thereby falling into the problem that traffic fluctuation cannot be quickly reflected.
Furthermore, with remarkable progress in information communications technologies, it will be more and more difficult to exactly estimate traffic condition, and the optimization design technology based on a specific traffic condition can no longer be effective.
Explained below is the conventional technology relating to the demand for communications over a designed communications network, that is, relating to a communications network managing method. In the conventional communications network, there has only been the concept of a physical network, and the physical network has a hierarchy of connection nodes such as a control center, a primary center, a toll center, an end office, etc. As a rule, primary centers are connected as if they were satellites to a control center, toll centers are connected as if they were satellites to a primary center, end offices are connected as if they were satellites to a toll center, and control centers are connected to one another to form a meshwork. Since the configuration matches the purpose of reducing the cost of transmission lines which occupies a large share in an entire cost of a communications system. Furthermore, there has been a single information medium and a rare change in the amount of information. Therefore, the traffic amount can be easily estimated, and the above described network can sufficiently meet the demand for communications.
Lately, there has been an increasing demand for data transmission and transmission via facsimile. In this case, though, a network is fixed each time a service is presented.
With an increasing number of digitalized telephone networks, a demand for a transmission via facsimile has considerably grown, and broadband communications in TV conferences have been increasingly requested. However, traffic has been dominated by services of less than the basic unit 64 Kb/s of telephone networks. Therefore, in N-ISDN, most settings indicate 64 Kb/s with a primary speed appropriately covered.
As information communications have been used widely in the fields of ordinary life, industrial activities, etc., the users' demand for communications services includes higher-level services such as:
1. High-speed communications services such as communications among LANs, transmissions of large files, HDTV, CATV, etc.; PA1 2. Requests for multimedia communications services from single-media communications services; and PA1 3. Requests for more flexible communications services.
Thus required are communications networks according to new concepts and functions.
On the other hand, the optical transmission technologies have advanced greatly and now prevail, and the costs for transmission lines have been reduced to a great extent, thereby causing communications business a problem that communications nodes should be configured more effectively.
Taking these demands and conditions into account, an asynchronous transfer mode (ATM) has been actively studied in various fields. In the B-ISDN, the ATM allows a plurality of media having different requisite bands to be integrally processed, and its standardization is earnestly requested internationally.
The features of the ATM reside in that:
(1) The concept of virtual path is introduced to establish a simple and flexible network. That is, a communications network is composed of a physical network and a logical network. The logical network can be designed flexibly.
(2) A user specifies one of a plurality of service qualities provided by the network and requests for communications (issues a call). In response to the call, the network determines whether or not the call can be connected.
On the other hand, the multimedia communications makes the estimation of the demand for traffic more difficult.
Therefore, in the communications network in the ATM, it is important to manage the resources flexibly and efficiently when a completely new method is realized in designing and managing the communications network, and the estimation of traffic demand is very difficult.
For example, a serious problem in managing an ATM network is that a single communications path, for example, a virtual path connection is provided between optional nodes in a network, or another path, that is, a detour path connection is permitted to meet the traffic demand in the network.
If only a single virtual path connection is permitted in a network, then a new transmission link is not searched for in response to a change in traffic condition, but the capacity in a predetermined transmission link is increased or decreased. It is an effective method providing for simplicity of a large-scale communications network accommodating multimedia traffic.
However, relating to the efficiency of the network, the traffic load actually applied to each communications node is not balanced well. Furthermore, the "burst" brings forth unequal service quality between different calls due to lack of a detour transmission link. Moreover, a busy transmission link prevents communications from being established even if there is another transmission link available, thereby reducing the efficiency of the network.
If, to solve the above described problems, a detour is permitted to all communicable transmission path connections in response to a large number of communications connection requests which cannot be accommodated in a predetermined transmission link, then there is the problem that an undesirably long time and a large amount of control are required to select detour transmission path connections as the network grows larger in scale. Thus, the network fails to flexibly respond to a change in traffic.
Furthermore, even if detour paths are established between optional nodes in an ATM network, that is, communications paths of a limited number, for example, virtual paths are established, there is no specific method of selecting communications paths meeting a change request from among a plurality of communications paths in response to the communications capacity change request between optional nodes. Therefore, much time has been taken for experimental selection of detour paths.